Structured data is information that is highly organized (e.g., an Excel spreadsheet). In the world of business intelligence, structured data is preferable because it is easy to connect to and search, especially when stored in a relational database. Compiling this data and preparing it for analysis is also easy to accomplish.
On the other hand, unstructured data (e.g., an email) does not work well in a database format. It lacks organization and consistency, making it difficult to store, compile, and prepare for analysis.